Future development of the maximum luminance of LEDs

Flashlight Modding and DIY Parts
81

Yeah, but CELNM1.TG has a tiny thermal pad. And it doesn’t make up for this with smaller thermal resistance inside the package - actually it’s a bit worse here too. So likely it won’t be possible to overdrive it so much.

This also has a much smaller thermal pad than the older LED.
Due to better efficiency I find it interesting, but I don’t expect it to beat Q8WP.

It’s interesting that now we’re discovering several years old emitters that are great for our application.
And sad how the later generations are often just inferior for what we do.
And what’s worse - we’re not a big enough market to even keep an old product alive, let have one developed for us.

82

BTW, I don’t see it mentioned:
There’s some chance that Luxeon F turns out good.

83

I think the most realistic way to get higher luminance is with a Q8WP using higher bins.

84

Oh you’re right, I wonder why the CELNM1 has a higher stock output then, if it’s basically the same die.
The CELNM does have higher thermalresistance due to the smaller pad, but what’s cool is that the CSLNM actually has less thermal resistance than the black flat.
.
For the CSLPM1 even though it has a smaller thermal pad it is still the same size as the CSLNM1 and has the same thermal resistance as the Q8WP, so it might not be that difficult to cool well.
.
So in summary:
LUW HWQP: White 3.05 W 325 lm 108 cd 1000 mW 334 mW/sr 120° = reference
KW CSLNM1.TG: White 3.00 W 325 lm 108 cd 1000 mW 334 mW/sr 120° = same contact pad size, lower thermal resistance
KW CELNM1.TG: White 3.00 W 374 lm 124 cd 1150 mW 384 mW/sr 120° = small contact pad, higher thermal resistance, for some reason better performance at stock? will not work on any normal MCPCB

LE UW Q8WP: White 4.20 W 533 lm 153 cd 1650 mW 473 mW/sr 130° = large contact pad, lower thermal resistance than black flat
(die size 1.91mm^2)
KW CSLPM1.TG: White 4.20 W 515 lm 171 cd 1590 mW 529 mW/sr 120° = same contact pad size as black flat, same/slightly lower thermal resistance as Q8WP (much lower than black flat)
(die size: 1.99mm^2)

85

I just noticed something interesting about the Black Flat:
It only has one bond wire. In his test Köf3 noted that one of his Black Flats died at 5.4A because the bond wire melted. So we can conclude that it can tolerate up to ~5A. This also means that it gets warm at currents close to that. This might be one reason why the Vf of the Black Flat is so high at high currents, which of course makes it run hotter than it would otherwise.

The Cree XP-G2, XM-L2, XP-L (HI/HD) and Luminus SST-40 all have two bond wires. The latter goes up to 9.5A.
Now of course we don’t know if they use bond wires with different diameters 8Cree might have reduced the diameter of the XM-L2 bond wires at sme point because they now die at lower currents than in the past).

I do think it’s interesting though that the Osram Q8WP has not two, but four, very thick looking bond wires. They should not be heating up nearly as much as the single one in the Black Flat.

86

I run all my black flats at 6-6.5A though…

87

That’s a good point, I had forgotten about your use of high currents.

88

That is still a mystery for me ?

Cause of the tests the Black Flat is running best at 4,5A.

Do you make other tests and the Led get brighter with more A ?

Regards Xandre

89

Here are the results Enderman posted back then. His voltage measurements seem incorrect though (way too high), there was probably some additional resistance involved.

The problem here is that he can't really prove why his LEDs performed better in that setup. You can only test it for yourself by emulating parts of the process (his specific thermal paste, active cooling, his way of soldering etc.).

90

I tested my own black flats with a fan cooled, copper plate, 5 heatpipe CPU cooler and MX-4 thermal paste.
I was getting lux increases up to 5.2 amps which was the limit on the power supply, and the curve showed it kept increasing a bit past that.

And yes as the driver said the voltage measurements are off by a lot, I didn’t measure the voltage at the LED properly, that was the voltage at the power supply.

The buck drivers I use are 6A, but they can spike up to 6.5A according to mtn electronics. I think last time I measured the current I get about 5.7-5.9A stable out of them
I have killed one or two black flats by turning them on max too fast for the first time.
If I go to low, then medium, then high after a few minutes there are no problems. After some use it seems like I can quickly turn it to max with no issues.

I want to do a new test using liquid metal, but first I need to buy a power supply that can do more than 5.2A.
I’m planning to get the DPS5020 soon.

91

I just found an interesting, old test of diamond thermal grease here .

92

Yesterday it occurred to me that Oslon Black HWQP has a 2.7 mm² thermal pad and 4 times as much exposed ceramic.
Could we harness it to improve heat extraction efficiency?

BTW, the table in the fist post shows 3,06 mm². In the datasheet I see 2.7x1 mm minus rounded corners.

93

Thanks, I changed it to 2.67mm2 (using 0.1mm corner radius). I wonder why I had that value there. I think I might have accidentally used an older version of the H9QP datasheet.

First we need to understand the internal layout of these LEDs. The Black Flats use the UX:3 Technology. There is a pdf on this somewhere.

94

Here is an interesting interview of some Osram OS employees from 12-2016 (in German).

They talk about Osram Stage LEDs. The white variants of these LEDs have new kind of ceramic-phosphor on top. It does not contain silicone and instead is sintered, compressed and baked at 1000°C. It is supposed to tolerate higher temperatures better and does not show signs of degradation.

They also consider 2mm2 die size at high-currents to be an innovation.

The UX:3 technology is a different way of getting the current to the die. Instead of putting a wire mesh on top (which reduces light output and adds electrical resistance), they input current from the bottom side and spread it inside the semiconductor. This also results in a more even current distribution.

EDIT: I found it, the paper regarding the development of the UX:3 technology: Development of high-efficiency and high-power vertical light emitting diodes (2014).

Generally this technology seems to have been a very big step for Osram. It caused big jumps in performance and the current Black Flat and Q8WP are definitely already highly optimized LEDs for high luminance and reliability.

The lower resistance of the current spreader caused a reduction in Vf of the LEDs compared to older models.

Interesting statement: "The maximum power of the devices is only limited by the resistivity of the current distribution layer and the current density of the n-contacts, which can both be engineered according to the application requirements."

Another one: "Owing to the low-Rth(<1.4 K/W for a 1mm2 chip) design, formed by a silicon carrier with solder die attached, the maximum current can be maintained up to 150 °C junction temperature."

That thermal resistance is a lot lower than the value in the datasheet of the Black Flat.

The LE UW Q8WP seems to be the 2mm2 SHP (super high power) chip they talk about there, the largest variant of the technology at that point. It looks exactly like their diagrams (except for only being 1.8mm2).

95

Thanks, interesting.
Though I don’t understand it nearly well enough to be able to recognise the thermal paths, let alone estimate their resistance to the ceramic…

96

You could try sanding down the bottom of the LED, but it will be difficult. Saabluster managed to do it with the Cree XR-E because that LED actually also has contacts on top. This enabled him to just sand down the entire LED.

These Osram LEDs don’t have those, so you would need to sand down only the center solder pad.

97

Speaking of Osram Stage…

LE RTDUW S2WP has 1.8 mm² white die (and 3 others that we can ignore).
Specs look largely like a quad Q8WP, quarter thermal resistance, four times thermal pad size. Actually marginally worse than that.
Now…if a single die can’t widen its thermal path to use that of neighbouring dies, it should be slightly worse than Q8WP.
However if it can move some meaningful heat through the other parts of the package, it could be a winner.

98

That’s an interesting idea, but very impractical! Centering the white die of that LED will be “fun”. It seems to have the same die and lumen range of the Q8WP.

99

You surely know this stuff much better than I do…could you please elaborate why is it going to be significantly harder to centre than Q8WP?
I would think that with both lights having their dies offset would cause the same kind of troubles. OK here the die is offset in 2 dimensions.

100

Well it has a non-standard solder footprint. It wont center itself correctly when you put it on a pcb for 5050 (XM-L etc.) LEDs. The next problem you will have (which has nothing to do with focussing though) is that the solder connections underneath for the indvidual dies have a really impractical layout for this scenario. Anode and kathode of a single die are on the same side of the LED. So soldering it onto a 5050 pcb will not work.

Many people wont drill new holes for correct centering when modding a flashlight. You might need to even drill new holes in the light, not just in the pcb. With Q8WP you just need to widen the holes a bit. But I’m not sure, maybe it’s not so bad after all.

It also depends on what kind of light you want to build or mod. The bigger the reflector, the more headaches little things like this will give you.